One of the books on my writer's reference shelf is Cassell's Modern Guide To Synonyms & Related Words, which I bought in a secondhand used books store on the Kloveniersburgwal. I have several dictionaries, but you often need context. Cassell's book gives examples to distinguish between synonyms, so you learn the difference between sardonic and sarcastic.

I think, after reading many self-published dreck, that books like these should be mandatory reading for writers.